Assuming that water vapour is an ideal gas, the internal energy change $\mathrm{\Delta }U$() when 1 mol of water is vaporised at 1 bar pressure and 100° C, (Given : Molar enthalpy of vaporization of water at 1 bar and $373\mathrm{K}=41\mathrm{kJmol}{\mathrm{mol}}^{-1}$and $R=8.3{\mathrm{Jmol}}^{-1}{\mathrm{K}}^{-1}\text{ ) }$ will be: